Colorado Residential Wireman Exam Preparation

Below are a few questions from your upcoming PSI state exam:

1. What would be the calculated volume allowance for the following equipment?
   • • • One switch connected with two 12 AWG conductors
       • One switch connected with two 14 AWG conductors
   • Correct Answer: NEC – 314.16(B)(1-5) Box Fill Calculation, Table 314.16(B). Calculate the following: 
   • Switch #1 connected to the 12 AWG wires: 2 x 2.25 = 4.50 cu-in.
   • Switch #2 connected to the 14 AWG wires: 2 x 2.00 = 4.00 cu-in.
   • Two (2) 12 AWG conductors: 2 x 2.25 = 4.50 cu-in.
   • Two (2) 14 AWG conductors: 2 x 2.00 = 4.00 cu-in.
   • Sum total = 17.00 cubic inches.
2. What is the calculated minimum ampacity rating of the branch circuit conductors given the following residential appliance?
   • • • Power: Single-phase
       • Operating Voltage: 120 Volts
       • Nameplate Rating: 1,400 Watts
   • Correct Answer: Using the Ohm’s Law Formula Wheel: I = P/E = 1,400 Watts / 120 Volts = 11.67 amperes.
3. Using the optional method of service calculation, calculate the size (in amperes) of a 120/240-volt service disconnecting means when the total load of a one-family dwelling is 67,500 VA (ignoring or excluding air conditioning loads as well as heating loads)?
   • Correct Answer: 220.82, Example D2(a) Optional Calculation for One-Family Dwelling, see steps below.
   • Subtract 10 kVA from the total load = 67,500 VA – 10,000 VA = 57,500 VA.
   • Multiply the remainder by 40% = 57,500 x 40% = 23,000 VA.
   • Add the 10 kVA back to the derated portion = 23,000 VA + 10,000 VA = 33,000 VA.
   • Calculate current load: I = P/E = 33,000 VA / 240 V = 137.5 A.
   • Per Table 240.6(A) size up to a standard of 150 amperes.